Pet doors are a useful means for pets to enter and exit an indoor facility, while at the same time attempting to resist the invasion of unwanted creatures, people, and inclement weather. Pet doors have suffered from inclement weather, however, due to the nature of the rubberized flaps which allow the pet's entrance and exit. Winds, rain and snow can easily enter the flaps. Some devices and adaptations of pet doors have been proposed which are highly exclusive, and therefore not useful to many pets. Some devices are exclusive to the point of negating a pet's use of the pet door device. Most of these devices are also attached to the pet door or to the doorway which houses the pet door, not an always desirable adaptation for the indoor facility structure. What is needed is an apparatus which forms a removably placed vestibule adjacent to a typical pet door. The apparatus should not discourage pet use, and therefore is ideally transparent. The apparatus should not require a significant learning curve for the pet. Further, the apparatus should be collapsible. The apparatus should also be height adjustable in order to best align with a given pet door. The present apparatus provides these problem solutions.